Interleaved soft switching bridge power converter

ABSTRACT

An interleaved soft switching bridge power converter comprises switching poles operated in an interleaved manner so as to substantially reduce turn-on switching losses and diode reverse-recovery losses in the switching pole elements. Switching poles are arranged into bridge circuits that are operated so as to provide a desired voltage, current and/or power waveform to a load. By reducing switching turn on and diode reverse recovery losses, soft switching power converters of the invention may operate efficiently at higher switching frequencies. Soft switching power converters of the invention are well suited to high power and high voltage applications such as plasma processing, active rectifiers, distributed generation, motor drive inverters and class D power amplifiers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to switch mode power converters, andmore particularly, though not by way of limitation, to soft switchingbridge power converters suitable for high power and high voltage DC-DC,AC-DC and DC-AC conversion.

2. Brief Description of the Prior Art

It is generally desirable to operate switching power supplies at thehighest frequency that is practical for a particular circuit. Operatingat higher frequencies allows inductor and capacitor values in a powersupply to be reduced, which reduces physical size and cost and alsoenables improvements in the transient response of the power supply.Reducing the energy available for delivery to load arcing, such asplasma arcs, is also a desirable goal. High-frequency operation allowsthe use of smaller output filter capacitors, which store less energythan larger capacitors, and this reduces the energy that can be suppliedto plasma arcs. Operating frequencies in switch mode power supplies thatutilize hard-switching power converters are limited, however, becausethe switching losses can become prohibitively high as the operatingfrequency is increased.

AC-DC and DC-AC bridge power converters typically comprise sets of oneor more simple pole circuits. In a hard-switched simple switching polecircuit, for example, a switching device is connected between positivepole and active pole terminals, and a second switching device isconnected between the negative pole and active pole terminals. Duringoperation of the pole circuit, the active pole terminal is alternatelyconnected between the positive and negative pole terminals as theswitches are turned alternately on and off. A full-bridge converterrequires two pole circuits, and a half-bridge converter has only onepole circuit. Bridge converters configured for multiphase operationcomprise multiple pole circuits; for example, a three-phasehard-switched bridge converter comprising three simple pole circuitswith three active terminals. Depending on how the hard-switched bridgeconverter it is configured and utilized, power may flow into or out ofthe active terminals. Switching devices of switching bridge convertersare typically realized with active switches (e.g. insulated gate bipolartransistors (IGBT), bipolar transistors, field-effect transistors) orwith diodes functioning as passive switches. In hard-switched convertercircuits, however, considerable losses may occur when an active switchin a simple pole circuit is turned on while a diode in the other switchof the pole circuit is conducting.

Various schemes have been designed to employ soft-switching inverterpoles using auxiliary switches in order to avoid switching losses inpower converters. In addition to requiring auxiliary switches, suchsoft-switching bridge schemes typically include resonant circuits thatadd additional cost and incur losses due to circulating currents.

Class D amplifier circuits use pole circuits to produce AC or DCvoltages or currents that change at rates that are slow compared to theswitching frequency. For example, class D audio amplifiers may employ asingle hard-switched inverter pole with its active terminal coupled to aload through an LC lowpass filter. Alternatively a DC-DC converter mayuse two hard-switched inverter pole circuits with active terminals thatare connected to coupled filter inductors. The poles circuits areswitched in an interleaved manner that reduces ripple in the outputcurrent, but the circuit does not provide soft switching.

Like class D amplifiers, opposed-current converters produce AC or DCvoltages or currents that change at rates that are slow compared to theswitching frequency. These converters may use compound pole circuitsthat consist of a positive pole circuit and a negative pole circuit. Thepositive pole terminals are connected together and the negative poleterminals are connected together. An inductor is connected between theactive pole terminal of each of the two inverter poles and a node whichserves as the active pole terminal for the compound pole circuit. Theactive switches in the positive and negative pole circuits are both onat the same time, and so considerable current flows in these inductorseven when there is no output current, resulting in low efficiencies.

SUMMARY OF THE INVENTION

This invention provides interleaved soft switching bridge powerconverters having interleaved soft switching poles. In general, aswitching converter of the invention comprises one or more switchingpoles connected to a voltage source. The poles are operated in aninterleaved manner so as to substantially reduce turn-on switchinglosses and diode reverse-recovery losses in the switching pole elements.

In one embodiment of the invention, a bridge power converter comprisesat least one composite or compound switching pole having a positive poleterminal, a negative pole terminal and an active pole terminal. Eachcomposite switching pole comprises a plurality of simple switching polescomprised of two switches connected in series and joined at an activeterminal, with each switch being either active or passive. Passiveswitches comprise a diode and active switches include an anti-paralleldiode. Each active terminal of each simple switching pole is connectedto an input terminal of an inductor assembly. The active switches in acompound switching pole are operated in an interleaved manner so thatthe action of an active switch being turned on during a switchconduction interval causes a diode in another switch to be subsequentlyturned off during a commutation interval. The active pole terminal ofeach composite switching pole is connected to a common terminal of theinductor assembly.

In accordance with various embodiments of the invention, compositeswitching poles are arranged into bridge circuits, such as half-bridge,full bridge, or poly-phase bridges. The positive pole terminals areconnected together to form a positive bridge terminal, and the negativepole terminals are connected together to form a negative bridgeterminal. The switches in the composite switching pole are operated tocontrol the flow of power through the bridge. Bridge converters of theinvention are operated so as to provide a desired voltage, currentand/or power waveform to a load.

By reducing switching turn on and diode reverse recovery losses, softswitching power converters of the invention may operate efficiently athigher switching frequencies. Soft switching power converters of theinvention are well suited to high power and high voltage applicationssuch as plasma processing, active rectifiers, distributed generation,motor drive inverters and class D power amplifiers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an interleaved soft switching circuit in accordancewith one embodiment of the invention.

FIG. 2 illustrates a repetitive-polarity interleaved soft switching polecircuit in accordance with one embodiment of the invention.

FIGS. 3-6 illustrate details of various embodiments of the inductorassembly IA of FIG. 2 that provide filtered current.

FIGS. 7-9 illustrate details of various embodiments of the inductorassembly IA of FIG. 2 that provide unfiltered output current.

FIG. 10 illustrates a repetitive-polarity interleaved soft switchingbridge power converter in accordance with one embodiment of theinvention.

FIG. 11 illustrates an alternating-polarity interleaved soft switchingpole circuit in accordance with a further embodiment of the invention.

FIG. 12 illustrates an alternating-polarity interleaved soft switchingbridge power converter in accordance with an embodiment of theinvention.

FIG. 13 illustrates a specific implementation of the repetitive-polarityinterleaved soft switching pole circuit of FIG. 1 in accordance with afurther embodiment of the invention.

FIG. 14 illustrates waveforms of the repetitive-polarity interleavedsoft switching pole circuit of FIG. 13.

DETAILED DESCRIPTION

FIG. 1 illustrates an interleaved soft switching circuit in accordancewith one embodiment of the invention. Bridge converter circuit BCcomprises switching pole circuits comprising switch assemblies SA₁,SA₁′, SA₂, and SA₂′. Each of switch assemblies SA₁, SA₁′, SA₂, and SA₂′comprises a switching semiconductor switching device S₁, S₁′, S₂, andS₂′, respectively, disposed in parallel with an anti-parallel diode.Switches S₁′ and S₂′ and switches S₁ and S₂ form first and second polecircuits, respectively, disposed across positive and negative voltagessupplied by voltage supply V_(in). Control circuitry (not shown) isconnected to the control terminals of switches S₁, S₁′, S₂, and S₂′ anddelivers control pulses to control opening and closing of the switches.First pole circuit comprising switches S₁′ and S₂′ has an active poleterminal connected to inductor L₁, and second pole circuit comprisingswitches S₁ and S₂ has an active pole terminal connected to inductor L₂.The outputs of inductors L₁ and L₂ are connected to main inductor L₀.The output terminal of the bridge converter circuit (the output ofinductor L₀) drives a load (not shown).

In a first switching cycle, switch S₁′ closes and positive current isconducted from voltage V_(in) source through inductor L₁ and maininductor L₀ to the circuit load. Switch S₁′ opens at the end of thefirst switching cycle, at which point the inductor current is conductedduring a second switching cycle through the anti-parallel diode ofswitch assembly SA₂′. Before switch S₁′ is again closed to continuedelivery of positive load current, switch S₁ is closed during a thirdswitching cycle. Current is conducted from voltage V_(in) source throughswitch S₁, inductor L₂, and inductor L₁ so as to provide controlledcurrent slope (V_(in)/(L₁+L₂) which recovers the anti-parallel diode ofswitch assembly SA₂′ with significantly reduced losses. Also, as aresult when switch S₁′ is again closed to continue delivery of positiveload current, the amount of current conducted through S₁′ that would beexperienced as reverse recovery current by anti-parallel diode of switchassembly SA₂′ is substantially reduced.

Similarly, when switch S₁ is opened, inductor current is conductedthrough the anti-parallel diode of switch assembly SA₂. When switch S₁′is closed to continue delivery of positive load current, shut-offcurrent with controlled slope (V_(in)/(L₁+L₂) is also provided to theanti-parallel diode of switch assembly SA₂ through switch S₁′, inductorL₁, and inductor L₂. This in turn reduces the reverse recovery currentexperienced by anti-parallel diode of switch assembly SA₂. Also, whenswitch S₁ is again closed the reverse recovery loss of anti-paralleldiode of switch assembly SA₂ is very low.

Control circuitry of bridge converter BC regulates the operation ofswitches S₁ and S₁′ in duration and phase so as to provide a desiredpositive current waveform to a load. Similarly, switches S₂ and S₂′ areoperated so as to provide a desired negative current waveform to a load.In a first negative switching cycle, switch S₂′ closes and negativecurrent is conducted from voltage V_(in) source through inductor L₁ andmain inductor L₀ to the circuit load. Switch S₂′ opens at the end of thefirst negative switching cycle, at which point the inductor current isconducted during a second switching cycle through the anti-paralleldiode of switch assembly SA₁′. Before switch S₂′ is again closed tocontinue delivery of negative load current, switch S₂ is closed during athird switching cycle. Current is conducted from voltage V_(in) sourcethrough switch S₂, inductor L₂, and inductor L₁ so as to provideshut-off current with controlled slope (V_(in)/(L₁+L₂) to theanti-parallel diode of switch assembly SA₁′. Similarly, when switch S₂is opened, inductor current is conducted through the anti-parallel diodeof switch assembly SA₁. When switch S₂′ is closed to continue deliveryof positive load current, shut-off current is also provided to theanti-parallel diode of switch assembly SA₁ through switch S₂′, inductorL₁, and inductor L₂.

Inductances L₁ and L₂ control the current slopes during switchingtransitions, thereby affecting the losses associated with diode reverserecovery currents. By choosing the values of L₁ and L₂, the amount ofthe residual diode current, and therefore any additional turn-on losses,can be controlled and minimized. Larger values of L₁ and L₂ generallyresult in smaller reverse recovery and residual currents, but thetransition times are longer. Hence, values are chosen to optimize thetrade-off between switching frequency, loss of duty cycle control range,and the total power loss of the converter.

Bridge converter BC is operated so as to provide a desired voltage,current and/or power waveform to a load. In one embodiment of theinvention, a bridge converter operates to deliver low frequency ACpower, for example at 60 Hz. In another embodiment of the invention, abridge converter operates to deliver power at mid frequencies or radiofrequencies, as for example to a plasma load.

In other embodiments of the invention, each of a plurality of bridgeconverters operates as an element of a multiphase power converter. Inone embodiment, each of three bridge-type converters as depicted in FIG.1 is disposed as one leg of a three-phase interleaved inverter. Asdescribed in connection with the embodiment of FIG. 1, switches of thebridge converters are operated and regulated in duration and phase so asto produce a three-phase voltage, current and/or power waveform at theoutput of the three-phase inverter at a desired output frequency.

FIG. 2 illustrates a repetitive polarity interleaved soft switching polecircuit RPSSP in accordance with one embodiment of the presentinvention. A composite pole circuit includes at least two bipolar simpleswitching pole circuits BSP1 and BSP2. Each bipolar simple switchingpole circuit has a first active switch connected between a positive poleterminal PPT and an active pole terminal APT, and a second active switchconnected between a negative pole terminal NPT and the active poleterminal.

Alternatively, additional pole circuits are connected, for a total of Nbipolar pole circuits, as indicated by the dashed connections to the Nthbipolar pole circuit BSPN. The positive pole terminal PPT of eachswitching pole is connected to a positive pole terminal PPT4, and thenegative pole terminal NPT of each switching pole is connected to anegative pole terminal NPT4. The active pole terminal APT of eachbipolar pole circuit, BSP1 . . . BSPN is connected to an inductorassembly, IA, at an inductive assembly input terminal, IAIT1 . . .IAITN. An inductor assembly common terminal IACT is connected to theactive pole terminal APT4 of repetitive polarity interleaved softswitching pole circuit RPSSP.

The embodiment of FIG. 2 allows use of multiple switches that can shareprocessed power, while still having reduced switching losses. Forexample, if the total number of switches in a converter circuit isdoubled, while the total power dissipation within the converter mayremain the same, the dissipation from any one switch is reduced by halfwhich may simplify cooling of the switches.

FIGS. 3-6 show alternative implementations of inductor assembly IA ofFIG. 2 when filtering of the current flowing in the active pole terminalis required. The inductances between pairs of inductor assembly inputterminals that are connected to a pair of consecutively operatedswitching pole circuits, L_(ii), is an important parameter in producingsoft switching operation. The inductance between an inductor assemblyinput terminal and the inductor assembly common terminal IACT, L_(ic),influences the magnitude of the ripple current flowing through theactive pole terminal of the soft switching pole circuit. Preferably, theL_(ii) inductance values are less than one fifth of the inductance ofL_(ic).

The inductor assemblies of FIGS. 3-6 can be constructed so as to havethe same inductances the between all corresponding pairs of theirterminals. If the inductances between the terminal pairs are equivalentfor various inductor assemblies, then the converter waveforms will alsobe equivalent for the same operating conditions, and the total energystored in each inductor assembly will be the same.

FIG. 3 shows an inductor assembly implementation DIA in which one of Ndiscrete commutation inductors LC1 . . . LCN is connected between eachinductor assembly input terminal IAIT1 . . . IAITN and an inductorcommon junction ICJ. A main converter inductor LM is connected betweenjunction ICJ and the inductor assembly common terminal IACT. In order toprevent excessively long commutation times, the inductance betweeninductor assembly input terminals IAIT1 and IAIT2 is preferably lessthan about one-fifth of the inductance of between each of theseterminals and the inductor assembly common terminal IACT. The inductanceof the commutation inductors in FIG. 9 is therefore preferably less thanone-ninth of the inductance of the main inductor LM.

FIG. 4 shows an inductor assembly SAIA that has N pairs of commutationinductors connected in a series-aiding coupling arrangement. Oneinductor is connected between each inductor assembly input terminalIAIT1A . . . IAITNA, IAIT1B . . . IAITNB and an inductor common junctionICJB. When more than two windings are used in this type of inductorassembly they must come in pairs, and the switching sequence must beordered so that every successive switching assembly in the sequence isconnected to a winding of opposite polarity. The two simplest ways ofimplementing the coupled commutation inductors LC1A-LC1B . . . LCNA-LCNBare to wrap the windings around the center leg of an E-core set, or towrap them around the same side of a C-core set. Each pair of commutationinductor windings is preferably tightly coupled (coupling coefficient ofat least 0.9). The inductances of the commutation inductor windings arepreferably nearly equal. The inductance between a pair of inductorassembly input terminals approaches four times the inductance of onewinding for tightly coupled windings that are connected in aseries-aiding arrangement. A main converter inductor LMB is connectedbetween an inductor assembly common terminal IACTB and the commonconnection between each pair of windings at an inductor common junctionICJB.

The peak energy stored in each of the commutation inductors LC1 . . .LCN of FIG. 3 is slightly less than the total peak energy stored in eachpair of the coupled commutation inductors IC1A-IC1B . . . ICNA-ICNB ofFIG. 4 when the inductances between their corresponding input terminalsare the same, the operating conditions are the same, and the peakreverse-recovery currents of the diodes are minimal in comparison todiode forward currents. Thus, the size of the coupled commutationinductors of FIG. 4 can be significantly smaller than the combined sizean equal number of the discrete commutation inductors of FIG. 3. Forequivalent inductor assemblies and equivalent operating conditions,there will be slightly more peak energy stored in the main inductor LMof FIG. 3 in comparison with the corresponding main inductor LMB of FIG.4 because the total peak energy storage for the two configurations mustbe equal. This minor increased energy storage requirement for LM,however, has a negligible effect on its physical size.

FIG. 5 shows an inductor assembly implementation CCIA that has threecoupled commutation inductors LLC1 . . . LLC3 that are intended to bedriven by three switching assemblies. The commutation inductors could beimplemented with three windings wound around three legs of a coresimilar to what is used in three-phase transformers. The magnitude ofthe coupling between each winding pair must be less than 0.5, so therelative size reduction possible with this configuration in comparisonwith three discrete inductors of FIG. 3 will generally be less than therelative size reduction possible for two tightly coupled windings ofFIG. 4 in comparison with two discrete inductors of FIG. 3. Onecommutation inductor is connected to between each inductor assemblyinput terminal IAICT1 . . . IAICT3 and junction ICJC. A main inductorLMC is connected between junction ICJC and the inductor assembly commonterminal IACTC.

FIG. 6 shows an inductor assembly SOIA in which two main inductorwindings LMD1 and LMD2 are wound on a common core structure with aseries-opposing coupling arrangement. There are no commutationinductors, but the diode commutation effect still occurs due to theleakage inductance between the two windings. The inductances betweeninductor assembly input terminals IAITD1 and IAITD2 and inductorassembly common terminal IACTD are preferably equal, and the inductancebetween the inductor assembly input terminals is preferably less thanone fifth of the inductance between an input terminal and the commonterminal IACT. These constraints imply that the coupling coefficient isat least 0.9. The copper utilization for the inductance assemblies ofFIG. 6 is not as good as for those of FIGS. 3-5 because the currents inthe main windings are discontinuous. The configuration shown in FIG. 4with one pair of windings is the preferred embodiment of the inductorassembly.

FIGS. 7-9 show alternative implementations of inductor assembly IA ofFIG. 2 when filtering of the current flowing in the active pole terminalis not required. FIGS. 7-9 show inductor assembly implementations DXIA,SAXIA and CCXIA that are similar, respectively, to inductor assemblyimplementation DIA, SAIA and XXIA except that the main converterinductors LM, LMB and LMC are not present. As with the inductorassemblies of FIGS. 3-6, the inductances between pairs of inductorassembly input terminals that are connected to a pair of consecutivelyoperated switching pole circuits, L_(ii), is an important parameter inproducing soft switching operation. The inductance between an inductorassembly input terminal and the inductor assembly common terminal IACT,L_(ic), is not intended to provide filtering. The L_(ii) inductancevalues are significantly greater than the L_(ic) inductance values.

While the previously described preferred values of the ratios betweeninductance values in the various implementations of inductor assembly IAare derived from typical diode commutation times and typical ripplecurrent levels in the main inductors, they are merely guidelines forillustration, and not primary design constraints.

FIG. 10 shows a repetitive-polarity soft-switching bridge powerconverter RPSSB in accordance with a further embodiment of theinvention. This type of converter is used in applications such as activerectifiers and motor drives where the output polarity of the currentflowing in the active bridge terminals changes at a rate that is muchslower than the switching frequency. A repetitive-polaritysoft-switching bridge power converter RPSSB comprises at least onerepetitive-polarity soft-switching pole circuit. FIG. 10 shows athree-phase converter with soft-switching pole circuits RPSSP1-RPSSP3.The positive pole terminal PPT of each switching pole is connected to apositive bridge terminal PBT1, and the negative pole terminals NPT ofeach switching pole is connected to a negative bridge terminal NBT1. Inone embodiment of the invention, the SPA switches connected between thepositive pole terminal and an active pole terminal (SPA positionswitches) in each repetitive polarity soft switching pole operate in analternating manner for a first time interval and then the switchesconnected between the negative pole terminal and an active pole terminal(SNA position switches) operate in an alternating manner for a secondtime interval. In another embodiment of the invention, the SPA switchesand SNA switches in each simple switching pole are alternativelyswitched on and off, and the switches of corresponding positions (i.e.SPA or SNA) in different simple switching poles are switched in aninterleaved switching pattern.

The active pole terminal APT of each soft-switching pole circuit isconnected to an active bridge terminal ABT. The switching patterns areadjusted so as to regulate power flowing between active bridge terminalsABT4-ABT6. A full-bridge converter requires two soft-switching polecircuits, and a half-bridge converter has only one soft-switching polecircuit. The inductor assemblies of FIGS. 7-9 can be used inapplications such as motor drives where the inductances of the motor areused to smooth the currents.

FIG. 11 shows an alternating-polarity soft interleaved soft switchingpole circuit APSSP in accordance with an embodiment of the invention. Analternating-polarity interleaved soft-switching pole circuit is acomposite pole circuit that includes a positive switching pole circuitsuch as PSP1 and a negative switching pole circuit such as NSP1.Positive switching pole circuits have an active switch in the SPAposition and a passive switch in the SNA position. Negative switchingpole circuits have an active switch in the SNA position and a passiveswitch in the SPA position. The positive pole terminal PPT of eachswitching pole is connected to a positive pole terminal PPT5, and thenegative pole terminals NPT of each switching pole is connected to anegative pole terminal NPT5. The active pole terminal APT of eachswitching pole circuit is connected to an inductor assembly, IAX, at aninductive assembly input terminal, IAITX1 . . . IAITXN. An inductorassembly common terminal IACTX is connected to the active pole terminalAPT5 of soft interleaved soft switching pole circuit APSSP. Inductorassembly IAX can be realized with the inductor assemblies of FIGS. 6-9.

FIG. 12 shows an alternating-polarity soft-switching bridge powerconverter APSSB in accordance with an embodiment of the invention. Thistype of converter is used in high-frequency inverter applications inwhich the output polarity of the current flowing in the active bridgeterminals changes at a rate that is equal to the switching frequency. Analternating-polarity soft-switching bridge power converter APSSBcomprises at least one alternating-polarity soft-switching pole circuit.FIG. 12 shows a three-phase converter with soft-switching pole circuitsAPSSP1-APSSP3. The positive pole terminal PPT of each switching pole isconnected to a positive bridge terminal PBT2, and the negative poleterminals NPT of each switching pole is connected to a negative bridgeterminal NBT2. The SPA and SNA switches in each alternating-polaritysoft-switching pole circuit operate in an alternating manner. The activepole terminal APT of each soft-switching pole circuit is connected to anactive bridge terminal ABT. The switching patterns are adjusted so as toregulate power flowing between active bridge terminals ABT7-ABT9. Powerregulation can be accomplished by of known methods such as symmetricaland asymmetrical pulse-width modulation; adjusting the phase anglebetween the voltages at active bridge terminals, and varying theswitching frequency. A full-bridge converter requires two soft-switchingpole circuits, and a half-bridge converter has only one soft-switchingpole circuit.

FIG. 13 illustrates a specific implementation RPSSP5 of therepetitive-polarity interleaved soft switching pole circuit of FIG. 2that uses the series-aiding coupling arrangement shown in FIG. 4 forinductor assembly IA2. FIG. 14 shows waveforms from operation of thecircuit depicted in FIG. 13. The voltage between active pole terminalAPT5 and negative pole terminal NPT5 is labeled as V_(APT5), and thevoltage between active pole terminal APT6 and negative pole terminalNPT5 is labeled as V_(APT6). The voltage between inductor commonjunction ICJ2 and negative pole terminal NPT5 is labeled as V_(ICJ2).The currents flowing from the commutation inductors into ICJ2 arelabeled as I_(LC2A) and I_(LC2B). The current flowing out of ICJ2 intoinductor LM2 into is labeled as I_(LM2). The waveforms of FIG. 14illustrates operation of the circuit of FIG. 13 for one switching periodstarting at time t₀, and ending at time T_(s), for an operating regimein which the active switching devices (SW5 and SW7) in the SPA switches(SPA5 and SPA7) are controlling the current flowing out of active poleterminal APT7, and the active switching devices (SW6 and SW8) in the SNAswitches (SNA6 and SNA8) are operating at essentially the same time asthe corresponding anti-parallel diodes (APD6 and APD8), which carry mostof the current and function as free-wheeling diodes.

Referring to FIG. 14, switching device SW5 is turned on at time t₀. Thecurrent through anti-parallel diode APD6, I_(APD6), is typically verysmall or possibly zero at this time, so the peak reverse-recoverycurrent I_(RAPD6) of APD6 is also very small or possibly zero. At timet₀, the current through diode APD8, I_(APD8), is equal to the currentthrough LC2B. After SW5 turns on, the current through it ramps up as thecurrent in diode APD8 ramps down toward zero. The slope of the currenttransition in amperes/second is equal to the voltage between thepositive and negative pole terminals divided by the commutationinductance, L_(ii). The value of L_(ii) should be selected to be largeenough to allow the reverse-recovery currents in the anti-paralleldiodes to be much smaller than the peak values of the forward operatingcurrents.

When SW5 turns off, the voltage at APT5 rings down immediately, and APD6begins to conduct, picking up the main inductor current I_(LM2).Depending on the operating conditions, there may be a small currentflowing in LC2B when SW5 turns off. If there is current flowing in LC2Bat that time, IAPD7 turns off with a small reverse-recovery currentshortly after SW5 turns off, and the voltage at APT6 rings down untilAPD8 begins to conduct. Switch SW7 turns on at time T_(s)/2, and becausethere is little, if any, current flowing through diode APD8 at thattime, SW7 turns on without a large current spike, just as SW5 did attime t₀. The current through commutation inductor LC2A reverses as APD6is being turned off, and when APD6 finally turns off, this currentcauses the voltage at APT5 to ring up until anti-parallel diode APD5conducts. When SW7 turns off, the voltage at APT6 rings downimmediately, and APD8 begins to conduct, picking up the main inductorcurrent I_(LM2). Depending on the operating conditions, there may be asmall current flowing in LC2A when SW7 turns off. If there is currentflowing in LC2A at that time, LAPD5 turns off with a smallreverse-recovery current shortly after SW7 turns off, and the voltage atAPT5 rings down until APD6 begins to conduct.

The magnitude and direction of the current flowing through active poleterminal APT5 is controlled by adjusting the duty cycles of SPA switchesSW5 and SW7 with respect to the duty cycles of SNA switches SW6 and SW8.Soft-switching pole circuit RPSSP5 can process power bi-directionally,and is therefore useful as both an inverter and a rectifier. Inalternative embodiments of the invention, RPSSP5 is used as a class Dpower amplifier.

The voltage at the active pole terminal with respect to the positive andnegative pole terminals is affected by the current flowing in the activeterminal in addition to being affected by the duty cycle of the switchesbecause of the effect of the commutation inductors. The average value ofthe voltage drop due to the commutation inductors is approximately equalto the average value of the current flowing out of active pole terminaltimes the inductance between the inductor assembly input terminals,L_(ii), divided by the switching period T_(s). This effect increases theimpedance at active pole terminal APT5 of soft-switching pole circuitRPSSP5. If the commutation inductance is sufficiently large, thisimpedance will allow soft-switching pole circuits to be connected inparallel without having to be concerned about current sharing issues dueto component tolerances.

In addition to the switching pattern shown in FIG. 14, during timeintervals when it is known that the current flowing out of APT5 will bepositive, it is possible to operate the SPA switches, SW5 and SW7, inthe same interleaved manner shown in FIG. 14 while not switching the SNAswitches, SW6 and SW8. Similarly, the SNA switches SW6 and SW8 can beoperated in an interleaved manner while leaving the SPA switches SW5 andSW7 off during time intervals when it is known that current will beflowing into APT5. In many cases, it may be difficult to predict exactlywhen the operating mode should be changed from switching the SPAswitches to switching the SNA switches or vice-versa. The switchingpattern of FIG. 14 avoids this difficulty.

Although specific structure and details of operation are illustrated anddescribed herein, it is to be understood that these descriptions areexemplary and that alternative embodiments and equivalents may bereadily made by those skilled in the art without departing from thespirit and the scope of this invention. Accordingly, the invention isintended to embrace all such alternatives and equivalents that fallwithin the spirit and scope of the appended claims.

1. A method of delivering power to a load comprising: a) providing aswitching circuit comprising a first switching pole circuit disposedacross positive and negative voltages supplied by a voltage supply and asecond switching pole circuit disposed across positive and negativevoltages supplied by the voltage supply; b) operating at least oneswitch of the first switching pole circuit so as to deliver a currentfrom the first switching pole circuit to a load; and c) operating atleast one switch of the second switching pole circuit so as to furtherdeliver current from the second switching pole circuit to the load, theoperation of the at least one switch of the second switching polecircuit interleaved with the operation of the at least one switch of thefirst switching pole circuit so as to substantially reduce a diodereverse recovery current in the first switching pole circuit.
 2. Themethod of claim 1, further comprising operating at least one switch ofthe first switching pole circuit so as to further deliver current fromthe switching circuit to a load, the operation of the at least oneswitch of the first switching pole circuit interleaved with theoperation of the at least one switch of the second switching polecircuit so as to substantially reduce a diode reverse recovery currentin the second switching pole circuit.
 3. The method of claim 1 whereinthe operation of the at least one switch of the second switching polecircuit is interleaved with the operation of the at least one switch ofthe first switching pole circuit so as to provide a controlled currentslope that recovers a diode of the first switching pole circuit withsubstantially reduced diode reverse recovery losses.
 4. The method ofclaim 3 wherein the current slope is controlled by at least one inductordisposed in a current path between the first switching pole circuit andthe second switching pole circuit.
 5. The method of claim 1 wherein thefirst and second switching pole circuits are disposed in a full bridgetopology.
 6. The method of claim 1 wherein the first and secondswitching pole circuits are disposed as one leg of a multiphase powerconverter.
 7. The method of claim 1, further comprising regulating theoperation of the first and second switching pole circuits so as toprovide a direct current output to the load.
 8. The method of claim 1,further comprising regulating the operation of the first and secondswitching pole circuits so as to provide an alternating current outputto the load.
 9. A power converter comprising: a) a first switching polecircuit disposed across positive and negative voltages supplied by avoltage supply and a second switching pole circuit disposed acrosspositive and negative voltages supplied by the voltage supply; b) atleast one inductor disposed in a current path between the firstswitching pole circuit and the second switching pole circuit; and c)control circuitry for operating at least one switch of the firstswitching pole circuit so as to deliver a current from the firstswitching pole circuit to a load and for operating at least one switchof the second switching pole circuit so as to further deliver currentfrom the second switching pole circuit to the load, the controlcircuitry interleaving the operation of the at least one switch of thesecond switching pole circuit with the operation of the at least oneswitch of the first switching pole circuit so as to substantially reducea diode reverse recovery current in the first switching pole circuit.10. The power converter of claim 9 wherein the control circuitryinterleaves the operation of the at least one switch of the firstswitching pole circuit with the operation of the at least one switch ofthe second switching pole circuit so as to substantially reduce a diodereverse recovery current in the second switching pole circuit.
 11. Thepower converter of claim 9 wherein the at least one inductor is disposedto provide a controlled current slope that recovers a diode of the firstswitching pole circuit with substantially reduced diode reverse recoverylosses.
 12. The power converter of claim 9 wherein the first and secondswitching pole circuits are disposed in a full bridge topology.
 13. Thepower converter of claim 9 wherein the control circuitry operates toprovide a direct current output to the load.
 14. The power converter ofclaim 9 wherein the control circuitry operates to provide an alternatingcurrent output to the load.
 15. A multiphase power converter comprisinga plurality of converter legs, at least one of the converter legscomprising: a) a first switching pole circuit disposed across positiveand negative voltages supplied by a voltage supply and a secondswitching pole circuit disposed across positive and negative voltagessupplied by the voltage supply; b) at least one inductor disposed in acurrent path between the first switching pole circuit and the secondswitching pole circuit; and c) control circuitry for operating at leastone switch of the first switching pole circuit so as to deliver acurrent from the first switching pole circuit to a load and foroperating at least one switch of the second switching pole circuit so asto further deliver current from the second switching pole circuit to aload, the control circuitry interleaving the operation of the at leastone switch of the second switching pole circuit with the operation ofthe at least one switch of the first switching pole circuit so as tosubstantially reduce a diode reverse recovery current in the firstswitching pole circuit.